Brain and spinal cord injuries can have a dreadful impact on the life of an individual. One approach to improving the individual's quality of life is to record brain activity, directly decode an individual's motor intentions, and then use this input to control robotic devices or reanimate the motionless muscles by microstimulation. While the use of brain activity to generate very simple actions has recently be demonstrated, there remain major obstacles that will need to be overcome before these methods can be used for effective therapies in paralyzed humans. One of these problems is the inability of planar probes to provide a 3-dimensional map of local neural activity. Tetrodes, formed by simply twisting 4 wires together and clipping off the end, are thus often preferred in primate studies over planar silicon (e.g. Michigan) probes.
The tetrodes are formed by simply twisting 4 wires together, thermally fusing the insulation, and clipping off the end. The ends may be electroplated to reduce the contact resistance. They have a critical advantage over planar silicon probes in that they can provide a 3-dimensional map of the local neural environment. However, there are many problems with the current technology: 1) electrical characteristics, resistance and capacitance, are not reproducible, 2) resistance is 3 very high-about 300 kΩ which causes a poor signal-to-noise ratio, 3) the insulation is leaky, 4) they cause significant tissue damage, and 5) the technology is not easily extended to a series of tetrodes at various depths along the shank.
An improved nonplanar multimodal neural probe and fabrication of such a probe that improves the reliability of tetrodes and supports the development of 3-dimensional electrical probes with ten to a hundred channels is discussed herein. The probe provides integrated electrode arrays on the surface of a fine tapered needle that can penetrate the brain with minimum damage. One way to reduce the contact resistance is to increase the area of contact without increasing the physical size of a contact. For example, a dense array of high aspect ratio gold pillars may be fabricate on the contact.
The improved nonplanar multimodal neural probe incorporates a surface enhanced Raman scattering (SERS) sensor at the probe's distal end. This may allow the probe to, for the first time, link the underlying neuronal electrical activity with the associated changes in the biochemical microenvironment near the probe tip. The neuronal activity is modulated by the local biochemical environment, and at the same time, the activity releases neurotransmitters and initiates cascades that change the local environment. An integrated lightguide on the side of the probe may deliver excitation light to the distal end of the probe and return Raman scattered light to a spectrograph-detector assembly outside the brain. A high-density array of gold columns may be fabricated at the lightguide exit and provide surface enhancement.